Protein Losing Enteropathy (PLE) is a poorly understood disorder that may accompany congestive heart failure. We studied a 14-year-old boy who developed PLE and thrombosis of the central vein 11 years after undergoing right atrial to pulmonary artery anastomosis (Fontan operation) for a univentricular heart. The results confirm a correlation between the administration of heparin and resolution of PLE. This effect does not occur following administration of LMWH.